Electrodynamic loud-speakers and microphones



March 2, 1965 G. R. PouToT 3,171,904

ELECTRODYNAMIC LOUD-SPEAKERS AND MmRoPHoNEs /oal zd E E- EMM/4 5 F 1E..E 1d ad 9d /Od 2d dw ad 1 EY INVENTOR GEORGES @055x27- Pol/TOT UnitedStates Patent O 3,171,904 ELECTRODYNAMEC LUD-SPEAKERS AND MICRPHONESGeorges Robert Pontet, 5 Rue Maillard, Paris Xl, France Filed June 19,1961, Ser. No. 117,987 Ciaims priority, application France, June 23,1960, 830,847 1 Claim. (Cl. 179-1155) My invention relates toimprovements in electrodynamic loud-speakers and microphones, It is awell known fact that, as concerns its fundamental components, thestructure of a loud-speaker is the same as that of a microphone, the twotypes of apparatus differing chiefly by the direction of operation: theloudspeaker produces vibrations of the atmosphere under the action ofthe electric oscillations to which it is subjected whereas themicrophone operates in a reverse manner and produces electricoscillations under the action of vibrations received from the outeratmosphere. Apart from certain details in structure which are well knownper se for any one skilled in the art, it is possible to consider themicrophone as the reverse of the loud-speaker and a large number oftechnical arrangements which are applicable to one type of apparatus arealso applicable to the other for reversed operation. For this reason andwith a view to greater clarity, I will no longer mention microphones assuch in the present specification while the expression loud-speakers isintended to convey also the meaning microphones so that the referencelto microphones should be implicitly understood after each expressionloudspeakerf It is also a well-known fact that a loud-speaker includestwo chief components of which one is transducer, that is an arrangementwith transforms electric oscilla* tions into mechanical vibrations,while the other component is constituted by a diaphragm which transmitsand diifuses the mechanical oscillations passing out of the transducerto the outer atmosphere.

It is a well-known fact that various types of loudspeakers are known inthe art, and electrodynamic loudspeakers are those wherein thetransducer is electrodynamic, that is, it resorts to the effects of amagnetic field on a current, with a view to transforming oscillatoryelectric energy into vibratory mechanical energy or reversely in thecase of microphones, in accordance with the well known law of Laplace.

The transducer forms furthermore the driving means for the loud-speakerand its effects are transmitted to the atmosphere through the agency ofthe diaphragm. The problems to be solved by those skilled in the art forsuch a transducer or driving means have, generally speaking, beenalready solved in a comparatively satisfactory manner. The case is notthe same for the problems relating to the diaphragm and chiefly to themanner of shifting the driving means with a view to obtaining throughthe agency of the diaphragm, a shifting of the largest amount of airpossible, with a maximum delity. Generally speaking, the diaphragm hasbeen hitherto constituted by a cone of paper or the like material, thearea of which adjacent the apex is made rigid with an electric windingforming part of the transducer, while the surface of said cone has aremaining area which is generally equal to one or more squaredecimeters, so as to provide for the shifting of a sufficient amount ofambient air.

The operation of such a system would be theoretically accurate if allthe points of the cone were to move in unison with 'the movable sectionof the driving means. But, in practice, the case is different, chieflyfor the high frequencies of the acoustic spectrum; this is ascrib- ICCable to numerous reasons which it is not necessary to disclose in thepresent specification, since anyone skilled in the art is wellacquainted therewith.

My invention has chietiy for its object, to provide loud-speakers ormicrophones which satisfy better than those employed heretofore thevarious requirements appearing in practice, and chiefly, they includediaphragms which are more faithful and/or more efficient, or are moreadvantageous than the known diaphragms.

My invention has for its object to provide a loudspeaker or microphoneof an electrodynamic type, which includes at least one magnet generatinga magnetic field acting on at least one conductive part such as a wireor ribbon which is rigidly secured to the actual diaphragm ensuring acoupling between said wire or ribbon on the one hand, and thesurrounding air on the other hand. Said diaphragm is made of anon-conductive material the thickness of which is sufficient foreliminating practically any elasticity within the range of accelerationsand/ or stresses appearing in the loud-speaker or microphone, saidmaterial having furthermore a specific weight which is under 0.1 andeven, preferably under 0.02.

According to my invention, such a loud-speaker is advantageouslycharacterized by the fact that said conductive wire or ribbon is laid onthe so-called rear surface of the diaphragm which surface faces themagnet or magnets, while at least 50%, and even preferably at least ofthe length of said ribbon, wire or the like conductive part, is insertedin the actual gap of Said magnet or magnets.

The material used for the diaphragm and referred to hereinabove isadvantageously a synthetic resin, preferably in an expanded conditionwhich bestows it with an extremely low specific weight and moreparticularly the material preferably is expanded polystyrene.

ln a preferred embodiment, the diaphragm of such a loud-speaker ormicrophone has a large front surface with reference to its thickness,while the major part of its rear surface is rigid with the movableelements of the transducer or driving means of the loud-speaker or thelike, said movable elements being Substantially linear. The thickness ofthe diaphragm is preferably between 3 and l2 millimeters.

On the other hand, the material forming the diaphragm and the thicknessof the latter (excluding any possible projecting section carry-ing theconductive wire, ribbon or the like part), are advantageously such thatany force applied to the rear surface of said diaphragm excluding suchpossibly projecting sections may, within the range of accelerationsand/or stresses appearing normally in loud-speakers and microphones, betransmitted without any substantial deformation to any point of thefront surface of the diaphragm which extends within an angle of lessthan 50 to either side of the perpendicular to said rear surface,passing through the point of application of the force to be considered.

According to a particular embodiment of the invention which seems to beof special advantage, the coupling is performed, by means of aconductive ribbon or wire, which is given longitudinally the shape of acurve rep resenting rectangular relaxation oscillations, which curve istermed hereinafter a Greek pattern. Said ribbon is rigidly secured tothe diaphragm. The front surface of the latter may assume any desiredoutline, but preferably it has a rectangular outline, the length andbreadth of which are several times the thickness of said diaphragm. Thevarious sections of the Greek pattern are however energized allsimultaneously by a number of magnets, the poles of which extend over aline the length of which is greater than their spacing. Said conductiveribbon or Wire is carried on the rear surface of the diaphragm, as

Hof FIG.V l1,

1- My invention will beoreadily understoodupona reading of the followingdisclosure relating to V,embodiments illustrated in theaccompanyingdrawing,.which,includes diagrammatic views of said embodiments andwherein FIGS. 1 and 2 are sectional Views, respectively through lineIV-I ofFIG. 2 and .lijneII-ll ofFIG. 1 of a loudspeaker in accordancewith a preferred embodiment of my invention,.

^ Y FIG. 3 .is a partial detail View on enlarged scale' of theloudspeaker-illustrated Yin FIGS.' 1 and `2, Y

FIGS. 4 and 5 are respectively a transverse sectional View and alateraly elevational View of the chief components of a loud-speakerwherein the coupling is performed by means of a rectilinear ribbon,

FIGS. 6 and 7 aredetail views atrightangleswith each Aother and showing.means for connecting the conductive ribbon :of FIGS. 4 and 5,

i FIG..S is a view. similar toFIG. 4 for the-.casefwhere the coupling isobtained through two movable parallel ribbons,

FIGS.. 9.and 10 .are two partial'cross-sectional views at right angleswith refe-rence to each other, respectively taken. along lines IX-IX ofFIG..8 and lines X--X ofi FIG. 8, y FIG. .l1 is a plany view fromunderneath of a coupling system having a. large area which is startedvibrating by a conductive ribbon in the shape of afGreek pattern,

FIG. 12 is a corresponding view along line XII- XII FIGS. 13 and 14arepartial views respectively in transverse cross-section` and viewedthrough the rear surface of the diaphragm -of the main components of aloudspeaker wherein the coupling is obtained through a plurality ofwindings.

.It should be .understood that these figures andthe cor- .respondingparts of the disclosure are Agiven solely by way of example, and by nomeans in a limiting sense.

In the various gures, the following elements o ,f the embodimentsillustrated, which play the. same .part,. have received `the samereference numbers followed by an alphabetic. index-which differs fromone figure to another. Thus,

The reference number 1 designateslmy improved dia- Phragm, v

The ,reference numberv Z'Mdeslignates Vthe ,movable con- 4ductivesection of the drivingmeans or transducer, which movablesection isrigidlysecured to said diaphagml, Thereference numbers?? and designatethe poles or fractionsl of a pole of the transducer-energizing magnet ormagnets which have the'same polarity,

f VThe reference number 4 designates the poleof such ,a magnet, thepolarity of which is opposed to that of thepoles 3, and 5,

. The reference numbers 6, '7, 8 and 9 designate the sides of thetransverse cross-section ofthe diaphragm,

6 designating more particularly the so-called front side, .7 the rearside which may be omitted, 8 and 9 the lateral surfaces extendingbetween the front surface and themovable section of the driving means,

The reference numbers andll designate the parts (such as a ribbon, wireor winding, and the like said embodiment is constituted Aby a plate orsheetiof expanded polystyrene, the specific weight of which is 0.013

4 to 0.015 gram per cubic centimetenandthesize of which is 81 mm. alongits breadth l, while its length L is 120 mm. and its thickness e1 isequal to 6 mm. Inside said sheet or plate la, there .are provided (forinstance by a set of cutters) sixteen parallel'grooves or slots 14, thedepth of which is equal to 4 mm, and the breadth o -f which l1, is equalto 4 mm. Said` grooves Iarethus separated by projections or webs15,thebreadth I3 of said Webs being equal to l The front surface of thecoupling means thus formed is shown at 6u while its rear surface 7aincludes the webs 15. Over the outer'free edges of said webs 15, thereis positioned and secured a conductive wire 2a, the cross-sectionofwhich may be round or flat. Said vwire which is advantageously ofaluminium is inthe case considered, a round wire of a diameter of about0.5 mm. Preferably, the Wire 2a is previously subjected to the action ofa template which gives itthe shape of a Greek pattern (as shown at 2g,2h, 2z' etc. in FIG. 11) while one of the surfaces of said, Greekpattern, and possibly also the free edge of the webs are coated withasuitable glue, so that the positioning and the securing of thecontinuous wire 2a over thesuccessivewebslS, may be obtained accuratelyand rationally. This latter gluing operation is performed`advantageously by means of the abovementioned template. Whenuthe gluehas set, the template is removed, and the uends of the wire 2a areconnected with yielding conductive braids 16 or the like adapted toprovide the desired electric connections vof the wire.A A A At the. twoends of the diaphragm 1a, (FIG. 1) considered longitudinally, thereareassembled, for instance A through gluing, two tongues 12a, 13a. whichprovide for the suspension of the diaphragm 1a with reference to theframe 18a-18b-2j5af25c of thearrangement. This enlsures an accuratepositioning ofthe diaphragm, whereby its teeth or webs may engage freelythe magnetic gaps lformed in tl 1e transducer; said gaps are provided inthe mannerl disclosed hereinafter, in a manner such that said webs4 maymove inside said gaps and execute a rectilinear translational movement(in the vertical direction appearving in,FIG. 2), whereby they carryalong with them the as more particularly favorable, the use of polyvinylchlorideor Polyurethane, preferably in `an expanded condition, and thesizes of which are in the example considered, alengthof 81 mm., abreadth l2 of 8 mm. and a thickness of 2 mm. These tongues connect, inthe present case,

' the diaphragm 1 z withtwo metal members 19a, 1917 having a squareshaped cross-section. Said members 19 may be disconnected and adjustedwith reference to the Aframe 18a 18 tg, 25a, 25b of the arrangement.Insulated 1 conductive terminals 20a, 20b, 'pass through saidmembers Y,19 and ensure the feed of current to the conductive braids The magneticcircuit of the transducer or driving means includes in the embodimentdescribed magnetic slots 21,

vtherlumber of whichis equal to that of the webs 15, and

consequently, in-the present caseth 'ei r number'is equal to seventeen.Each of said slots is provided with a useful gap of which the sizes are:breadth I4 (FIG. 2) 2 mm.-

. height h (FIG. 2) 4.5mm., length v(FIG. 1) 1l8 mm. The field in eachof said gaps is equal to about 2,000 gauss,

and is obtained as follows:

v Between two blades 22 and 23 of a highly magnetic i metal sheet,.of athickness of 0.5 mm., of a length of 118 plate projects by 1 mm'.beyon'd'the small blades'ZZ fand 23 .along three of the sides of"the"lat'ter, whereas "on the fourth side, that is, at the upper side in FIG.2, there is provided between the successive blades 22 and 23 a usefulgap forming a sort of slot 21. Finally, the blades 22 and 23 formthrough their upper edges the poles 3 and 5 of the energizing magnets.

As far as the details of execution of the magnetic section of thearrangement are concerned, it seems of advantage to proceed as follows:firstly seventeen members which are identical with that which has justbeen described are executed, each including two small blades 22 and 23and a small ferrite plate 24. These seventeen members are then assembledwith a spacing between them of 2 mm. which allows the free flowing ofair behind the diaphragm that is, at the lower ends of FIGS. 1 and 2 bymeans of two comb-shaped structures 25a and 25b advantageously ofaluminum including the desired corrugations or utings, for engagementover the outwardly projecting ends of the different ferrite plates.

These two combs 25a and 25h serve as stays for the longitudinal anglebars 18a, 18h (FIG. 2) which form with said combs 25a and 2512 theabove-referred to frame of the loud-speaker. The whole arrangement isdesigned furthermore in a manner such that the webs of the diaphragm areinserted each substantially at mid-height into the corresponding gap orslot 21 and thereby the wire 2a is adapted to move in a magnetic fieldwhich is unvarying during the movements of the diaphragm.

As already mentioned, the above described embodiment illustrated inFIGS. l to 3, may be subjected within the scope of the accompanyingclaims to various modifications, of which a number are disclosedhereinafter.

According to a rst modication which is very advantageous in many cases,instead of the webs 15 carrying a conductive element constituted by awire, there is provided a conductive element constituted by a metalstructure, also in the shape of a Greek pattern cut in a thin plate,preferably of aluminium and glued atwise over the free edges of saidwebs, as clearly shown in FIG.3. This may lead to an easier or moreconvenient machining, taking into account the desired accuracy to beobtained. It may furthermore be preferable to give the breadth I3 of thecorresponding webs of the diaphragm a value generally larger than 1 mm.,say about 2 mm.

According to a further modification, instead of producing a windingwhich in practice extends in an unvarying direction between the twobraids 16, there are formed, for instance by means of a template,windings including a plurality of forwardly and rearwardly directedsections of a conductive wire which is then generally of a smallerdiameter than the wire 2a. This allows obtaining driving or transducingmembers of which the impedance may be higher than in the embodimentillustrated in FIGS. 1 and 2.

According to a still further modification, there are produced in asimilar manner, two or more windings which are mechanically associatedbut are electrically insulated from each other, for instance with a Viewto tapping oit a counter-reaction voltage adapted to control thetransducer and the associated amplifier. Such a counter-reaction systemwould be of no interest in the case of conventional loud-speakersbecause the movements of the cone provided in the latter have noaccurate relationship with the movements of the driving windings. Thecase is quite diiferent in the case of a loud-speaker according to myinvention, wherein the movements of the diaphragm are exactly those ofthe conductive section of the driving means and wherein consequently theinterest of such a counter-reaction system may be considerable.

With the various embodiments of my improved loudspeaker or microphone,the following further features are advantageously incorporated:

The front surface 6a of the diaphragm 1a is smooth in the manner of aplate, and its surface sizes, that is its length and its breadth whensaid surface is rectangular,

range between eight times and fifty times the thickness e1 of saiddiaphragm including its webs such as 15.

The actual breadth I3 of each web 15 ranges between 20% and 100% of saidthickness e1 and the depth of each web measured in the same direction ase1 ranges between 30% and 70% of e1.

'The thickness of the diaphragm 1a without the webs, is such that theforces applied to its rear surface by the webs 15 starting from theconductive wire or ribbon may be transmitted without any substantialdeformation to the correspondent point of the front surface 6a of saiddiaphragm, any point of said front surface being located through theactual structure of the diaphragm and its webs, within a virtual angleof less than 50 to either side of a line perpendicular to the rearsurface, and passing through the point of application of the force to beconsidered. This arrangement is disclosed with further detailhereinafter, reference being made to FIG. 8.

The point of application of the force is to be understood as the pointat the root of a web, more particularly along its outer surface as shownat A or B in FIG. 3. It will be appreciated from a consideration of theembodiment of FIGS. 1-3 that since the thickness of the diaphragm fromthe front to the back surface is 2 mm., and the clear spacing betweenthe web is 4 mm. (these dimensions will be documented more particularlyhereinafter) that an angle drawn from A or B to a point on the frontsurface of the diaphragm midway between the webs will be inclined at anangle of 45 whereby every point on the front surface of the diaphragmwill lie on the base of an isoceles triangle having base angles of 45and a vertex located at points A or B.

The thickness of the diaphragm in FIGS. 1-3 is equal to e1 minus thedepth of the webs which as shown on page 5 is equal to 6 mm.-4 mm. or 2mm. The spacing between the webs is specified at page 5 as being l1which is 4 mm.

FIGS. 4 and 5 relate to a `further embodiment of my improvedloud-speaker. The coupling is obtained by means of a rectilinearconductive ribbon 2d of which the plane registers with the medial planeof the gap between the magnet poles 3d and 4d inside which gap theribbon is engaged. Said ribbon may be given any allowable desiredlength, for instance l0 to 30 cm. or more. It is therefore insertedthrough one of its edges inside the gap of a corresponding magnet 3d,4d. Near its other edge, it engages in a suitable manner the apex of adiaphragm 1d according to my invention, having a cross-section, theshape of which approximates that of a triangle with a front surfaceshown at 6d, while its sides 8d and 9d converge towards theabove-mentioned apex, thus forming advantageously an angle t of aboutThe feed connections for the ribbon 2d thus held in the diaphragm areshown at 11d and the tongues for the suspension of the coupling 1d areshown at 12d. FIGS. 6 and 7 show in full detail an advantageousembodiment of the connections lttd, which play the same part as 11d.Said connections 10d are formed by an undulating section 2d of theloud-speaker driving means in a plane perpendicular to that of FIG. 7,together with the feed of current into the conductive ribbon 2d.

As to the suspension tongues 12d, they are advantageously made of ayielding and light material, as in the case of the tongues 12a and 13aillustrated in FIGS. l and 2. Said tongues connect the diaphragm withthe frame of the loud-speaker, or else with the case or baiiie board ofthe latter if any, which is however no longer necessary in the case ofloud-speakers according to my invention.

In all cases, the suspension tongues for the diaphragm of a loud-speakeror a microphone according to my invention should have desiredyieldingness and/ or elasticity so that the movements of said diaphragmmay constitute translational movements parallel with the correspondingplanes of symmetry of the gaps in the magnets.

. sponding thereto.

electro dynamiccoupling is performed by means of'a Wire or ribbon'whichvis wound or formed into a'rectangular or substantially rectangularshape, of which the longer sides 2e andaZf are several times longer thanthe'breadth of the rectangle or substantially rectangular iigure corre-These two larger sides 2e and 2f are inserted respectively in' one ofthe two gaps extending between the poles, 4e on the one hand, and 3e,'5eof a magnet on the other hand. The remainder of the embodiment issubstantially the same as in the case of FIGS. 4 and 5, except asconcerns the transverse cross-'section'of the diaphragm le; saidcross-section is in the present case substantially that of an isoscelestrapezium of which the smaller base forms a section of the rear surfaceof the diaphragm. Near the ends of said smaller base, are fitted thesections 2e and '2f of the operative conductive ribbon, which is fed bytwo connections e made of a further pleated ribbon, of which the meanplane is perpendicular to the plane of the rectangular structure e and2f. Considering a predetermined length of the diaphragm 1d or 1e(measured perpendicularly to the plane of FIGURES 4 and 8), the frontsurface of the diaphragm 1e lof FIG. 8 may have an area which issubstantially double that of the diaphragm 1d of FIG. 4, said diaphragmremaining furthermore perfectly rigid and faithful, taking into accountthe fact that the geometrical conditions'as to the angles are observedin this case infa manner similar-to that which has been disclosed forasimilar purpose, in the case of the embodiment of FIGS. 1 to '3. VThismay be explained in a clearer manner as follows (FIG. 8): the

vforces being applied to lthe points'A and B of the rear surface '7e ofthe diaphragm, by the conductive ribbons'ze and 2f, any point P whateveron Vthe front surface 6e of the diaphragm lies within avertical'geometrical-angle (which therefore does not correspond to amaterial' stru'cture inside the diaphragm), whichangle' is'equal at amaximum to "50 to either side of the perpendiculars AB or DEto said rearsurface passing throughsaidpoints A and D. In the case'of a point P(FIG. 8),'it`is'apparent that the latter lies bothin the angle `BAC=aVYandsinside the angle EDF =d, these two^angles 'being equal to less lthan50".r Experiencehas shown that Ysuchl ageometrical condition relating toall the points of the -frontsurface of the diaphragm with reference toAthel points ofapplication of forces on the rear surface of the' lattercorresponds to an absence of any substantial deformation of thediaphragmwhich 'appears then as quite rigid and incapable of moving without anydeformation or phasefshift-ing withl reference to its rear surface. Thiscooperates consequently inthe obtention of high'A grade results bymyimproved' loud-speaker or microphone, Ysaid high grade beingmodifications proposed for the latter figures. Eachof the long sides ofthis Greek patternis :inserted insidefthe corresponding gap of a magnetwhichis' not illustrated, in a manner similar to what has beendisclosedv with-referenice to FIG. 8.

Lastly, FIGS. 13 and 14v relate to a loudspeaker-according to theinvention, wherein the coupling is-obtained by means of a number ofcircular windings. In FIG. 13, are shown in particular two of saidwindings,2m and 2n,

positioned in the circular gaps oftwo Acorresponding mag- G0' Thecontrol of said Adiaphragm 1b`is obofqsaid windings-2m, 2n, 2p, 2q areshown.

u nets 3m,\4m, 5m, and Sn, 411, and Sn. In FIG. 14, four Preferably thediameters of said windings (which are equal tosay 2 cm.) aresubstantially equal to one half of the spacing of their axes. Thediaphragm is shown atlm. It may have a large area as inthe case of FIGS.1 and 2; the

linear sizies of said area depends merely on the number of windingssuchA as 2m, Zn to be positioned on the rear surface 7m of vsaiddiaphragm, in a manner such that the latter may move rigidly asa unitand without any, parasitic or distorting elfects as already mentionedhereinabove.

ThusLwhatever may be the embodiment adopted, my invention provideselectrodynamic loud-speakers and microphones, executed in a novel mannerand provided with substantial advantages among which I wish to mentionmore particularly the very large useful areas provided by the frontsurface of the diaphragm 1 which I obtain, in association with afaithfulness in the reproduction and/ or in the coupling, which is farsuperior to what was usually obtainable hitherto; this invention alsoprovides a very simple and sturdy structure of a comparativelyv low costprice, considering the high grade of operation and advantageous featuresreached.

As already mentioned, my invention is by no means limited tothose'applications or embodiments of its different parts, which havebeen more particularly disclosed and it covers, in contradistinction,all the modifications thereof, falling within the scope of theaccompanying claim, and for-instance, in case ofan embodiment similar tothat of FIG. 11, the openy rectangular sections of the ribbon 2g, 2h, 2ineed not be all interconnected, the successive longer'sides of saidrectangles beingV in fact, if

desired, all independent of one another, and also it is possibleto'resort, as required, to sizes or numerical'data which are differentfrom those mentioned with reference to the examples disclosed chiefly in-the case of the examples illustrated in FIGS. 1 to 3.

In Vthe accompanying claim, the expression"electrodynamicapparatusfshould Ybe construed as including elec- "trodynamicloud-speakers yand electrodynamic microphones.

What I claim-is: i Sound reproducing'apparatus ofthe electrodynamic.type comprising a diaphragm of expanded synthetic -resin having aspecic weight less than 0.1 gram per cubic centimeter, said diaphragmhaving a front and rear surface which are substantially parallel to oneanother, said front surface being aflat planar surface, said diaphragmincluding lintegral equally spaced rectangular webs extendingrearwardly` from the rear surface of the diaphragm and'dening a seriesof equal spaces between adjacent webs,sa1d webs beingspaced apart adistance such that the spaces Vtherebetween are substantially equal tovthe distance which each web projects from the rear surface of thediaphragm'whereby said spaces between adjacent webs have a squareprofile, a continuous conductive element secured to said webs at alocation remote from the rear surface of`the"diaphragm, meanselastically supportingthe diaphragm topermit'rectilinear translational`movement thereof and"fixedly supported magnetic means 'including aplurality of magnetic elements equal in number to theiwebs'andhaving'magnetic gaps in which areV accommodatedrespective'webs, saidlmagnetic means and conductive yelement constituting a magnetic circuitin `rwhich variations in the magneticfield of the magnetic elementsproduces cor-responding 'displacement -of' the con- Vductive'elementaswell as ythe webs and diaphragm secured thereto,-said diaphragm havinga distance between the front and-rearsurface thereof which isrelated tothe size of fthe spaces between'adjacent webs such that every pointonthe front ysurface ofthe diaphragm lies on the base of at least oneisoceles` triangle having a Vertex at the intersection of the rearsurface of the diaphragm with Vthe edges of the webs and including avertex angleof less ythan whereby the diaphragm will undergo sub- 9stantially rectilinear translational movement as a result of variationsin the magnetic lield.

References Cited by the Examiner UNITED STATES PATENTS 1,604,532 10/26Riegger 179-1155 1,749,635 3/30 Gerlach 179-181 1,987,412 1/35 Neumann179-1155 2,297,218 9/42 Henrich et al. 179-181 2,978,669 4/61 Harris179-1155 kt\\ 2,978,671 4/61 Harris 179-1155 3,111,187 11/63 Barlow179-181 FOREIGN PATENTS Germany. Germany. Germany. Great Britain. GreatBritain.

OTHER REFERENCES Rigidity of Loudspeaker Diaphragms, Barlow, Decem- 10ber 1958, Wireless World, vol. 64, No. 12, pages 564-569.

ROBERT H. ROSE, Primary Examiner.

WILLIAM C. COOPER, Examiner.

